We propose to develop a novel gyro traveling wave tube amplifier (gyro-TWT) at 395 GHz with an output power of 500 W and an operating bandwidth exceeding 3 GHz and a small signal gain > 45 dB. The amplifier will be used in Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (DNP-NMR) experiments and Electron Paramagnetic Resonance (EPR) experiments. The output power of the proposed amplifier is three orders greater than those available from solid-state sources at similar frequencies and the operating bandwidth combined with the ability to coherently amplify complex input signals for use in DNP-NMR and EPR will enable new generation of pulsed DNP-NMR and EPR experiments that are currently impossible to perform with free running fixed frequency oscillators. This amplifier can upgrade the currently deployed dozens of gyrotron oscillators for use in DNP-NMR and provide researchers with the ability of conducting experiments with a broad range of polarizing agents without the need for a superconducting sweep coils in the NMR magnet. Also, the amplifier will enable researchers to explore the promise of pulsed DNP-NMR experiments. The proposed amplifier can be operated with a peak power 500 W with a duty factor of 10 % or in continuous wave mode with an output power of 50 W. In Phase I, we will design the amplifier system and perform detailed modeling and simulation of its performance using benchmarked state-of-the-art design codes used in microwave tube research. We will present a complete mechanical design of the system and verify the thermal and electrical properties using commercial finite element codes. We will also build and test the cold performance of the most important element of the system, namely, the interaction circuit and demonstrate its suitability for integration with the tube. These tests will be performed on a Vector Network Analyzer to verify the microwave propagation properties of the device. In Phase II, we will fabricate the electron gun, the internal mode converter and other auxiliary components such as microwave windows etc. The entire system will be integrated and tested in our laboratory to demonstrate the proposed output power and bandwidth.